The present invention relates to practical, inexpensive mortars and aluminous high temperature cements and concretes which will withstand multiple freeze-thaw cycles without crazing, cracking or spalling to a much greater degree than have the prior art materials. Mortar and concrete that are exposed to the freezing and thawing cycle, particularly in areas where water stands thereon craze and crack when subjected to freezing, and spall when thawed thereafter. The crazing becomes more pronounced and deeper as the mortar or concrete is exposed to successive cycles. This is a major cause of the deterioration of the concrete highway system in the Northern part of the United States, and hundreds of millions of dollars are required for patching operations each year in the areas where the freeze-thaw cycle exists.
It is an object of the present invention, therefore, to provide new and improved mortars and concrete which are competitive in price to that currently used for pavement and/or building products such as shingles, siding and panels, and which will withstand the freeze-thaw cycle with considerably less damage than have prior art materials.
The prior art has experimented with all types of reinforcing materials in mortars and concrete for the purpose of increasing its strength and in some instances to try to reduce the crazing and cracking produced by the freeze-thaw cycle. To my knowledge, reinforcements have not appreciably reduced the crazing and cracking but some hold cracked areas in place so that the spalling thereof is less apparent. Water in the cracked areas, however, when frozen, spreads the cracking regardless of prior art reinforcements, so that conventional reinforcements have not been the answer to the freeze-thaw problem.
Glass fibers are produced commercially in two general types, one being blown fibers, and the other being pulled fibers. Blown fibers comprise random lengths of twisted interlocking fibers that are formed into mats or batts. Pulled fibers are made by simultaneously pulling from 200 to 2,000 molten streams of glass, grouping them when solidified into a strand, and coiling them around a rotating drum to produce a package. These pulled fibers must be coated with a size before coming together, otherwise they will break when they pass over the winding apparatus that guides them onto the rotating drum. The sizes used in practically all instances are water base sizes which cool the molten streams and prevent the mutual abrasion.
Both types of fibers have been available for over 30 years and pulled glass fiber strand has been used extensively as reinforcements in plastics. They have not proven successful in reinforcing mortars and cements, however, because the strand which was commercially available in the past has been deteriorated by alkali attack from the lime that exists in Portland cement. From the work that was done with glass fiber reinforcements in thermoset plastics, it was learned that strand having high strand integrity gave the highest flexural strength, tensile strength and impact strength; while those strands which were loosely united gave inferior strengths. Practically all strand which was produced for reinforcing purposes therefore has been sized with aqueous emulsions of plastics. These plastics help prevent deterioration from alkali attack if they remain around the strand. Strands of even high strand integrity, however, are attacked by Portland cement. Recently, so called alkali resistant glass strands have been developed. These strands even though they survive for a number of years in Portland cement mortar and concrete do not overcome the freeze-thaw problem.
According to principles of the present invention, it has been discovered that: if glass filaments are used which have a water dispersible binder and a surface which is devoid of organosilanes or lubricants which permanently make the surface of the filaments hydrophobic; and if such filaments are chopped and agitated to substantially completely disperse the filaments generally uniformly throughout, the mortar or concrete will have vastly improved resistance to the crazing, cracking and spalling produced by the freeze-thaw cycle. This is accomplished when more than approximately 0.01 percent by weight of the strand, based on the solids of the mortar or concrete are utilized, and little freeze-thaw improvement is gained by using more than approximately 1.0 percent by weight of the strand. It has been found that 0.2 percent or less of such strand is the generally preferred amount, and that it is very difficult to incorporate more than approximately 1 percent of such strand into thick mortars or concretes. It has been observed that mortar or concrete utilizing the filamentizable strand dries out much faster than conventional mortar or concrete, or mortar or concrete that is reinforced by nonfilamentizable strand; and in fact, the mortar and concrete of the present invention utilizing the filamentizable strand crumbles excessively if the surface is not kept wet during the setting of the materials.
It is now theorized that due to the packing of the sand and/or aggregate, there are minute void areas throughout mortar and concrete in which water remains after hydration is complete. When the filaments of the present invention are not used, these voids may remain full of water or may become full of water, which when frozen, expands and produces crazing and cracking.
Since only filaments that are wetted by water produce the improvements discovered by the present invention, it is further theorized that the individual filaments are so numerous that they run through these void areas. In addition, they are so numerous as to in some instances touch each other, or are sufficiently close to each other that water from voids runs along the surface of the filaments from one to another until it reaches the surface of the material. Mortar or concrete that sets with such filaments in place may also tend to produce smaller void areas. Furthermore, even if the fibers are deteriorated by alkali attack so that their strength is greatly decreased, the skeleton of the filament remains to remove water from the center of the material by means of the surface energy of the glass.
It has long been known that glass surfaces which are not "poisoned" cause water to spread out almost indefinitely, and that the angle of contact of water on nascent glass or "non-poisoned" glass approaches zero. Individually dispersed filaments, therefore, pass through or are sufficiently close to all voids of the material that they extract freezable water therefrom. Any free water that remains does not fill the voids so that freezing does not produce cracking or crazing. Even glass filaments which are badly deteriorated by alkali greatly reduce the cracking and crazing normally produced by the freeze-thaw cycle. Preferably, however, the filaments will be of an alkali resistant glass, so that the filaments remain sufficiently intact to add to the strength of the material.